负电性纳米银溶胶SERS活性及稳定性的比较研究

用单宁还原硝酸银可制得表面带负电的、对阳离子型分子具有较强SERS效应的纳米银.为了进一步测试负电性纳米银溶胶的SERS活性及稳定性,在室温下用制针剂的封装机将样品(old NCS)封装并保存.两年后与新制备的负电性纳米银溶胶(new NCS)比较,用透射电镜观测发现old NCS与new NCS相比银粒子尺寸增大;用紫外可见吸收光谱测定old NCS的吸收峰为431 nm,new NCS的吸收峰为418 nm,old NCS与new NCS相比吸收峰发生红移.为比较old NCS及new NCS的SERS活性选取阳离子型分子、中性分子及阴离子型分子作为测试分子,用拉曼光谱仪测试这些分子在两种纳米银上的SERS谱,结果发现,阳离子型分子碱性品红、中性分子吖啶橙在old NCS及new NCS上SERS较强,阳离子型分子亚甲基蓝在oldNCS上与在new NCS上相比SERS较弱,阴离子型分子苯甲酸在old NCS及new NCS均未观察到SERS信号.

Comparative Study on SERS and Stability of Negative Silver Colloids

Negatively charged colloidal nano-silver particles were prepared by the colloidal chemical method. A 1.7% solution of silver nitrate(2 mL) was diluted with deionized water to 100 mL. A 1% solution of tannic acid(1 mL) was added dropwise to the solution stirring, then a 1% solution of potassium carbonate anhydrous(3-4 drops) was added to the mixed solution. Finally, a red-brown silver sol was obtained. It was testified that the silver sol is a negatively charged colloid by experiment of electrophoresis. The negative silver colloids (for short, old NCS) were kept on at the room temperature two year ago in order to test its SERS and stability. The sizes of particles were determined by Hitachi H-800 transmission electron microscope. Absorption spectroscopy and SERS were used to determine the main properties. Absorption spectra were obtained with UV-2401PC. Raman spectra were recorded with RENISHAW MIK 2000 Raman micro-spectroscopy. The 514.5 nm line of an argon ion laser with about 3 mw was used. Compared with the newly perpared negative silver colloids (for short, new NCS). It was found that the mean diameter of the old NCS was larger than the new NCS; old NCS had absorption maximum at 431 nm but new NCS at 418 nm, the absorbance spectrum of old NCS had a 12 nm red shift, and the red shift rate is about 0.5 nm/month; Both strong SERS spectra were observed when cationic molecules of fuchsine basic and neutral molecules of alcidine orange adsorbed on old NCS and new NCS; For cationic molecules of methylene blue, the SERS is stronger on new NCS than old NCS; but no SERS was observed for the anionic molecule of benzoic acid both on new NCS and on old NCS.